1. Field of the Invention
The present invention relates to a system and method for controlling fuel supply to an internal combustion engine which compensates for any imbalance between intake air and fuel quantities actually sucked into each engine cylinder due to their dynamic characteristics within an intake air system of the engine.
2. Description of the Prior Art
Conventional fuel supply control system for internal combustion engines are exemplified by Japanese Publication No. 53-102416, 55-35165, and 55-134718 the disclosures of which are incorporated by reference.
FIG. 1 shows a conventional fuel supply control systems for an internal combustion engine. In FIG. 1, numeral 1 denotes an air cleaner located upstream of an intake air passage 2, the intake air passage 2 being disposed between the air cleaner 1 and an inlet port of each engine cylinder 6. The numeral 3 denotes a throttle valve, and numeral 4 denotes an airflow meter which outputs an intake air quantity indicative signal S.sub.1 whose level changes according to an intake air quantity passing through the intake air passage 2. Numeral 5 denotes a fuel injection valve which injects fuel toward a corresponding engine cylinder 6. The amount of fuel injected depends on a pulsewidth of a fuel injection quantity indicative signal S.sub.5 to be described later. Numeral 7 denotes an engine speed sensor which outputs an engine revolution number indicative signal S.sub.2 in synchronization with the rotation of a crankshaft of the engine. In addition, numeral 8 denotes an arithmetic operation unit (ALU) comprising a microcomputer having a Central Processing Unit (CPU), memory such as a Read Only Memory (ROM) and Random Access Memory (RAM), and an Input/Output circuit. The arithmetic operation unit 8 receives various sensor signals including the intake air quantity indicative signal S.sub.1 and engine revolution number indicative signal S.sub.2, calculates an amount of fuel injected to the engine according to the current engine operating condition, and outputs the fuel injection quantity signal S.sub.5 to each fuel injection valve 5.
The arithmetic operation of calculating an amount of fuel to be actually injected through each fuel injection valve 5 in the arithmetic opertion unit 10 is carried out in the following manner.
Supposing that Q indicates an intake air quantity obtained by the air quantity indicative signal S.sub.1 measured by the airflow meter 4, N indicates an engine speed obtained from the engine revolution number indicative signal S.sub.2, and K indicates a correction coefficient, then a fuel injection quantity Tp (corresponding to a pulsewidth of the signal S.sub.5 sent to each fuel injection valve 5) is calculated as shown in the following equation: ##EQU1## wherein the coefficient K is a correction coefficient according to engine operating conditions, e.g., an engine temperature, etc.
As shown in the equation (1), the fuel injection quantity Tp is set chiefly depending on the intake air quantity Q and engine speed N with a correction factor of, e.g. engine temperature and concentration of an exhaust gas component by which the above-described basic fuel injection quantity is multiplied.
It should be noted, however, that the conventional fuel supply control system shown in FIG. 1 controls the fuel injection quantity by using the intake air quantity signal 4 outputted by the airflow meter S.sub.1 directly as a signal indicating the current intake air quantity and on the assumption that the injected fuel via the fuel injection valve 5 is sucked into the cylinder 6 without a time delay.
In other words, in the conventional fuel supply control system of FIG. 1 the intake air quantity Q is a measurement value obtained from is indicative of total engine intake air. The airflow meter 4 and the amount of fuel injected by each injection valve 5 which corresponds to the pulsewidth T.sub.p) injected into the intake air passage 2 and may not represent the amount of fuel actually sucked into each cylinder 6.
Therefore, although it is possible to accurately control the amount of injected fuel to the engine in a normal steady state, an error due to dynamic characteristics of the intake air and fuel supply occurs during operation in a transient state. Consequently, during transient operation, the air-fuel mixture ratio may deviate from a target value, adversely effecting fuel consumption, exhaust gas purification, and driving performance (drivability).